1. Field of the invention
The present invention relates to a method and/or a system and/or network devices for managing communication connections of a user equipment in a communication network. More particularly, the present invention relates to a method and/or a system and/or network devices providing an improved mechanism to release connections of a user equipment to the communication network when a communication session between the user equipment and elements of the communication network is to be ended.
2. Description of the Prior Art
Recently, an increasingly extension of communication networks, in particular of wireless cellular communication networks all over the world is taking place. Various organizations, such as the 3rd Generation Partnership Project (3GPP), the International Telecommunication Union (ITU), 3rd Generation Partnership Project 2 (3GPP2), Internet Engineering Task Force (IETF), and the like are working on standards for telecommunication networks and multiple access environments, such as GSM (Global System for Mobile communications), GPRS (General Packet Radio System), 3rd generation systems such as UMTS (Universal Mobile Telecommunications System), Wireless Local Area Network (WLAN), cdma2000 (code division multiple access) and the like.
In general, the system structure of a communication network is such that a subscriber's user equipment, such as a mobile station, a mobile phone, a fixed phone, a personal computer (PC), a laptop, a personal digital assistant (PDA) or the like, is connected via transceivers and interfaces, such as an air interface, a wired interface or the like, to an access network subsystem. The access network subsystem controls the communication connection to and from the user equipment and is connected via an interface to a corresponding core network system. The core network subsystem switches the data transmitted via the communication connection to a destination, such as another user equipment or another communication network. It is to be noted that the core network subsystem may be connected to a plurality of access network subsystems. Depending on the used communication network, the actual network structure may vary, as is known and defined in respective specifications, for example, for UMTS, GSM and the like.
Communication systems may operate on the basis of different transmission types. For example, a circuit switched (CS) communication and/or a so-called packet switched (PS) communication can be implemented, which are commonly known. Depending on the type the user equipment may simultaneously use both CS and PS communications, or either CS or PS communications at a time, or exclusively only one of CS or PS communications. Alternatively or additionally, there may be provided communication network structures operating on different communication frequency bands. Similarly, the user equipments may then communicate on one or both of these frequency bands.
In the case of a cellular mobile communication network, such as GSM or UMTS, the access network subsystems comprise specific areas, so-called cells, in which the user equipment is located. For example, the mobile communication network is designed to allow both a CS and/or a PS communication. One or more cells are covered by one or more transceiver station, for example a base transceiver station BTS (in case of GSM) or a Node B (in case of UMTS), via which the user equipment is connected to the network. A controller, such as a GSM base station controller (BSC) or a UMTS radio network controller (RNC), is provided in the access network subsystem for controlling one or more cells. In the case of a UMTS network, the access network is called UMTS Terrestrial Radio Access Network UTRAN which comprises one or more Radio Network Subsystems (RNS), while the GSM access network comprises one or more Base Station Subsystem BSS. Depending on the communication type (CS or PS) which is used, the access network controller transmits the user equipment's data to a corresponding core network control element, that is a Mobile Switching Center (MSC) in a CS case or a Serving GPRS (General Packet Radio Service) Support Node (SGSN), to which it is connected.
Current network structures may be designed to comprise types of communication systems (multi-type communication networks). For example, a combination of GSM, GPRS and UMTS network systems in one communication network is planned. This means, for example, that GSM, GPRS (2nd generation) as well as UMTS (3rd generation) access network structures, such as BSSs and RNSs, are controlled by a combined core network comprising 2nd generation as well as 3rd generation core network elements, such as SGSNs and MSCs.
For the establishment of a communication path for a user equipment in the communication network to a destination, connections and resources in the communication network are provided between the user equipment and the core network subsystem via the respective interfaces. This includes, for example, the allocation of one or more radio access bearers (RAB), and the like, to the communication session.
In the case of a UMTS communication network, for example, the user equipment is connected to a UTRAN RNS through a so-called Uu interface to a Node B and from there to the corresponding RNC. The connection of the user equipment to the UTRAN comprises a Radio Resource Control (RRC) connection providing signaling capability between them. An UTRAN RNC is connected to the core network through a so-called Iu interface. Depending on the connection type (CS or PS), the link of the connection path leads to a core network's SGSN or MSC. For the signaling between the UTRAN and the core network, i.e. for the Iu interface, Radio Access Network Application Part (RANAP) is used. RANAP supports the functions of Iu interface by signaling procedures as described, for example, in the 3GPP specification TS 25.413 V5.2.0 (September 2002). RANAP comprises, for example, control information for the radio network layer of the UTRAN protocol and basic control procedures. Amongst others, the RANAP protocol has the following functions:                Relocating serving RNC. This function enables to change the serving RNC functionality as well as the related Iu resources (RAB(s) and Signaling connection) from one RNC to another.        Overall RAB (Radio Access Bearer) management. This function is responsible for setting up, modifying and releasing RABs.        Release of all Iu connection resources. This function is used to explicitly release all resources related to one Iu connection.        
These functions are implemented by one or several RANAP elementary procedures described, for example, in the 3GPP specification TS 25.413 V5.2.0.
When a session between the user equipment and the core network is to be ended, connections and resources in the communication network for the user equipment are released. This includes a release of the Iu interface. This Iu release procedure enables the core network (for example the serving SGSN, MSC) to release the Iu connection and UTRAN resources related to a specific Iu connection of a user equipment. It can be initiated on the core network side, for example, due to a completion of transaction between the user equipment and the core network, UTRAN generated reasons such as a release request from the UTRAN (for example due to an unspecified failure, user inactivity, loss of radio connection with UE and the like), the completion of a successful relocation of the serving radio network subsystem, and the like.
Referring to FIG. 3, the release procedure for user equipment connections is described by means of a signaling flow. In this example, a PS connection is assumed. The core network's (serving) SGSN releases the Iu and the user equipment by sending a RANAP Iu release command message to the RNC. If there is no connection to the other core network, the normal procedure is that without any conditions the RNC releases the resources related to the signaling connection and the user equipment. In other words, the RNC can release the RRC connection if no (other) Iu signaling connection remains. For example, if the SGSN sends the RANAP Iu Release Command, but the UE still has an Iu signaling connection towards the MSC, then the RNC must not send RRC Connection Release to the UE, but informs the release of the SGSN (PS domain) signaling connection otherwise to the UE since the MSC may still need the RRC Connection. When the MSC sends RANAP Iu Release Command and there is no Iu signaling connection towards the SGSN anymore, then the RNC can send a RRC Connection Release to the UE, because no Iu signaling connection remains. This means that the RNC executes also a RRC connection release procedure by transmitting and receiving corresponding messages to and from the related user equipment in order to release the user equipment resources in good cooperation with the user equipment. A corresponding procedure is described, for example, in the 3GPP specification TS 25.331. In other words, after receipt of the Iu release command message, the RNC clears related UTRAN resources and returns any assigned Iu user plane resources to idle. Furthermore, the RNC sends a RANAP Iu release complete message to the core network (here the SGSN), by which the release procedure is terminated. Even though FIG. 3 shows the transmission of the RANAP Iu release complete message after the completion of the RRC release procedure, it is also possible that the RNC must not necessarily await the result of the RRC connection release before a confirmation for the Iu release can be transmitted to the core network.
However, this connection managing procedure for releasing a connection of a user equipment with the core network entails a load for the radio path and requires a specific capacity of the involved network elements and interfaces. In particular in a situation where the user equipment is not reachable for the UTRAN via which the core network and the user equipment were connected to each other hitherto, a waste of resources may take place.